Preheat the oven to 375°F. Line two muffin pans with 16 cupcake liners; set aside.
Make the cupcakes
In a large bowl, whisk together the flour, cornstarch, baking powder, cinnamon, and salt.
In the bowl of a stand mixer (or in a separate large bowl using a hand mixer), beat the butter until it's light and creamy, about 2 minutes. Then add the sugar and beat together until light and fluffy, about 3 to 4 minutes.
Gradually beat in the eggs, one at time. Then add the Fireball and the vanilla.
Slowly add the dry ingredients to the wet ingredients and add the milk. Mix together just until combined.
Use a cookie scoop to scoop out the batter and fill each prepared cupcake liner about ¾ of the way full with batter.
Bake at 375°F for 5 minutes. Lower the heat to 350°F and bake for 18-22 minutes, or when a toothpick inserted into the center of a cupcake comes out clean.
Allow the cupcakes to cool in the pan for 5 minutes. Meanwhile, make the frosting.
Make the frosting
In the bowl of a stand mixer or a large bowl using a hand mixer, beat the butter until creamy. Gradually add 1 cup of powdered sugar at a time, and beat together. Then add the cinnamon and mix just until combined.
Add the heavy cream, Fireball, and vanilla and beat until combined and smooth
Transfer frosting to a piping bag. Once the cupcakes have cooled down a bit, pipe the frosting on top and top with sprinkles, if desired.
Notes
Makes 16 cupcakes (21+ recipe)Storage: store frosted cupcakes in an airtight container at room temperature for up to two days or in the refrigerator for up to four or five days. Or, store unfrosted cupcakes at room temperature for up to five days, and store the buttercream in a separate container in the refrigerator for up to five days. Fireball: Fireball is a cinnamon-flavored whisky you can find in most liqueur stores. You can use any other cinnamon-flavored whisky you like. To make this kid-friendly, skip the alcohol and make a simple syrup with cinnamon sticks and substitute 2 tablespoons of the cinnamon simple syrup for the Fireball.Frosting: If your frosting is too thick for your liking, add a little more heavy cream or milk. If it is too thin and runny, add a little more powdered sugar.